ASR technologies enable microphone-equipped computing devices to interpret speech and thereby provide an alternative to conventional human-to-computer input devices such as keyboards or keypads. Many telecommunications devices are equipped with ASR technology to detect the presence of discrete speech such as a spoken nametag or control vocabulary like numerals, keywords, or commands. For example, ASR can match a spoken command word with a corresponding command stored in memory of the telecommunication device to carry out some action, like dialing a telephone number. Also, an ASR system is typically programmed with predefined acceptable vocabulary that the system expects to hear from a user at any given time, known as in-vocabulary speech. For example, the ASR system may expect to hear command words such as Call, Dial, Directory, Exit, Delete, or the like, such as at a main menu dialog with the user.
In contrast, out-of-vocabulary speech occurs when a user speaks a word or subword that is not within the predefined vocabulary of commands, numerals, keywords, or nametags. Out-of-vocabulary speech is particularly frequent when a user is not familiar with the predefined acceptable vocabulary. For example, a novice user may speak out-of-vocabulary saying something like “Okay” instead of an expected word like “Yes” and the ASR system may incorrectly interpret the speech as some other expected command word like “Goodbye”. Accordingly, the ASR system may process the incorrect command, or may repetitively ask the user to repeat the command. In either case, the user becomes frustrated. One solution to this problem is to audibly prompt the user with acceptable commands at every juncture in ASR dialogs. But this approach is too repetitious and frustrates users who are already familiar with the acceptable commands.